Certain he had never watched, let alone shared the movie, John contacted a solicitor for legal advice at a cost of £150. Then earlier this week, he received a second letter to say the accusation had been dropped.

In a missive signed "Davenport Lyons" rather than by an individual lawyer, the London-based firm wrote: "After further consultations with your internet service provider and our client regarding this matter, our client has decided to take no further action against you.

"You may treat this matter as closed. We would like to apologise for any inconvenience or distress this matter may have caused."

John doesn't consider the matter closed, however. He said: "I am now wondering if I should now send Davenport Lyons an invoice for my time and expense in this matter."

Davenport Lyons' client in its pornography copyright infringement business is the German firm Digiprotect. Smut producers signed over their copyrights to Digiprotect, which then harvested IP numbers from BitTorrent swarms seen sharing their output. Davenport Lyons then obtained orders at the High Court requiring ISPs to hand over thousands of customers' personal details.

When John contacted his ISP, the Post Office, it denied having received a demand for his home address. It transpires that his details were held by BT, which operates the entire Post Office broadband operation, including the billing.

Happy to get an apology, John had planned to fight Davenport Lyons anyway. Since it began demanding money to avoid embarrassing court action (a model it first ran on behalf of videogame producers in 2007), the firm has never tested the strength of its evidence in court.

In December, the Solicitor's Regulatory Authority said it would investigate a complaint that Davenport Lyons' letters "make incorrect assertions about the nature of copyright infringement" and "ignore the evidence presented in defence". That followed Atari's decision to drop the videogame infringement cases Davenport Lyons brought on its behalf.

Davenport Lyons did not immediately respond to our question as to whether it had had a rethink on its pornography copyright infringement practice. ®

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Update

Davenport Lyons sent this short statement, indicating its interest in pornography copyright infringement remains active: "Davenport Lyons continues to approach each case of alleged illegal file-sharing on an individual basis."